Tubes... and Biasing

[Schu]

If am I making a jump to QUALITY pieces... I do not want ANY extranious parts or circuits between me and my music... nothing. Bare bone striped down point to point goodness, period.

Edited June 21, 2014 by Schu

[oldtimer]

You guys make tubes sound like so much fun! I can wait forever before I get one!

[tube fanatic]

Well, maybe at one time. But today, we have billions of DVD players, CD players, receivers and other small audio appliances that run for decades with a very, very impressive MTBF. The devices we have today when operated from proper supplies are pretty immune to spikes. Not to say there aren't failures of course, but the statistics are way favorable on the whole!

The overwhelming advantage that can be obtained in modern circuits with such devices make it quite compelling for improving sound, but of course not for everybody, that's for sure! Some people enjoy staying with the antiques and that's a cool choice too. Have one on me!

I certainly can't disagree on those points Mark! My beliefs on the subject are probably regional- i.e. most of my TV repair work was in a very high lightning strike area (a beach community) with overhead powerlines. Although I'm now inland, this area also experiences unbelievable numbers of cloud to ground strikes which frequently take out not only consumer electronics devices, but also appliances with solid state controllers (stoves, dishwashers, and so on). Now I'll take you up on your offer and go have one (or two)!!! This is an enjoyable discussion Mark. Glad you started it!

Maynard

[Fjd]

My other difficult amplifier is a pair of Electra-print original 300b/6A3 DRD mono blocks. Those amplifiers have a big 5K ohm 50W power resistor that is adjustable by using two wipers. The biasing is done by moving the wiper on the variable power resistor while measuring the voltage drop change across a 10 ohm resistor. Another twist to this is that everything is inside the chassis where it is diffiult to reach unless the amps are turned over.

Well, that's an interesting amp. The good news is that bias is not so critical on SET amps and there's no compelling need to be checking it very frequently, as with p-p amps. May I ask who built this amp?

I believe these amplifiers were built by Jack Elliano long before his Electra-Fidelity website operation and before Bill Gaw reviewed the next version of the 300b DRDs for "Enjoy the Music." The review was a two-part article that can be found in the links below. You may have already seen it, but I also have a link to Jack's current 300b DRD schematic below. I believe the person I bought the amps from may have been selling them for an estate and I've had them for maybe six or seven years now.

http://www.enjoythemusic.com/magazine/viewpoint/1101/aachapter27.htm

http://www.enjoythemusic.com/magazine/viewpoint/1201/aachapter28.htm

http://www.electra-print.com/300bdrd.php

[eth2]

MY VAC's have LED's. You simply turn a set screw until the LED turns green. Could not be simpler.

[oldtimer]

It could be simpler eth. No screw turning needed with a high quality solid state amp.

[muel]

I kind of like checking the bias. For me it is a small part of my involvement with the audio experience and partially satisfies my need to fiddle with stuff. It is certainly not nearly as involved as setting up a turntable! I do get a little bored as I go month after month and find that the bias is rock solid every time and needs no adjustment. I'm not complaining though!

[erik2A3]

Jack Eliano also contributed to Vacuum Tube Valley. That's where I believe he first shared his schematic and discussed the DRD, so-called, design, it uses an unusual connection on the output, as also does the parallel or shunt feed we discussed previously, but is not the same. He calls it "Ultrapath". Also like parallel feed outputs, the Ultrapath was done a very long time go by.....who was it...Western Electric? General Electric? Can't remember which, now. I had done research into the technique, and it is quite old. The so-called Ultrapath capacitor is the large one (motor run type) shown under the chassis in the Electra-print amplifier. Eliano stated in the VTV article that he thought those capacitors were measurably more sensitive to low level detail, and having built both a DRD 45 and DRD 2A3, would say that detail retrieval is certainly one of the characteristics of the circuit.

Mark: I had just read Art Dudley's review of that Japanese amplifier in Stereophile and was interested in looking it up. We don't see that level of point-to-point wiring involvement very often any more. I was impressed by the craftsmanship, and some OTLs are much more complex than both more conventional and common PP or SE designs. His wiring reminded me of old Marantz and LEAK stuff. Do you recall the Marantz 10B tuner? The wiring in those things was phenomenal. But so to was the build quality of the enormous WWII era Hallicrafters and Hammarlund receiving and transmitting radios -- which were built and soldered together by extraordinarily skilled workers, many of whom were women.

Anyway, Dudley described the amp is being among the very finest he's heard. Just thought I'd share the wonderful craftsmanship.

[Fjd]

Jack Eliano also contributed to Vacuum Tube Valley. That's where I believe he first shared his schematic and discussed the DRD, so-called, design, it uses an unusual connection on the output, as also does the parallel or shunt feed we discussed previously, but is not the same. He calls it "Ultrapath". Also like parallel feed outputs, the Ultrapath was done a very long time go by.....who was it...Western Electric? General Electric? Can't remember which, now. I had done research into the technique, and it is quite old. The so-called Ultrapath capacitor is the large one (motor run type) shown under the chassis in the Electra-print amplifier. Eliano stated in the VTV article that he thought those capacitors were measurably more sensitive to low level detail, and having built both a DRD 45 and DRD 2A3, would say that detail retrieval is certainly one of the characteristics of the circuit.

Erik, I find the detail retrieval is excellent with these amps too and Jack had rated them at 13 wpc over the traditional 8 wpc that most get. In fact, it was listening to these amps that turned me around regarding the use of the 300b tube as this circuit does wonders with this tube.

While I have heard several implementations of the 45 tube, on my 'bucket list of amps' would be a pair of DRD 45 amps at some point, as I have not heard that implementation.

When I bought the Elliano 300b DRDs I had read just about everything there was to read regarding the amps and had stumbled upon, and read, your post below regarding the Western Electric's development of the circuit that Jack calls the ultrapath.

In addition, I did read in Affordable Audio (it looks like their site with back issues is gone again but found the issue on the electra-print site) where Jack also acknowledged the Western Electric design connection.

http://www.electra-print.com/docs/aa2006-05.pdf

A$$A: Can you explain in layman's terms what your circuit designs do differently than other companies?

JE: I've developed a number of designs, the first circuit design we revealed was using the cancellation of harmonic distortion of two consecutive stages of amplification by the use of each tube's matching transfer characteristics (look it up). They then would vector out there operational curves resulting in a very low distortion. An example is the grid of the power output tube was measured 4% from its driver tube, then a measured power output of less than 1%. This effect was first published by Sylvania in the late 30's then again in the 50's; it was lost until Cy Brenneman revealed it in our first article in Sound Practices as a very useful effect for this type of audio amp.

Second circuit design was the UltraPath or complete tube coupling to the transformer. We later found it to be common practice with Western Electric telephone repeaters dating back to the 30's. It is a very good and efficient way to reproduce high quality audio. We also saw this arrangement in one of the studio line amps.

Third was the Direct Reactance Drive or DRD which is an improvement on the old Loftin White. The circuit uses a minimum of parts and absolutely no encumbrances of coupling. The result is a very accurate power amp with a measurable increase of power level over the original Loftin White using the same tubes.

Fourth is a simple means to match an opamp to a grid. A very efficient nickel transformer design forces the opamp to deliver current instead of a voltage. In other words when you connect up to a CD player normally you are hearing the voltage of the opamp with no current flow to speak of, but when the CD players opamp output must now see a DCR of less than 1 ohm but and impedance held steady by a load resistance on the secondary. A voltage now appears on the transformer secondary load resistance as a result of opamp current. This current from the opamp is much closer to the published specs and it will usually perform more accurately. We called this the PVA or "Passive Voltage Amplifier". All of the above circuits, to the best of our knowledge, are not used by anyone, other than who we given permission.

Hi, Soren:

The variety of output coupling you outlined above is ANCIENT! And it is absolutely fascinating! I ran into this sort of choke-capcitor coupling this summer, while I was working on a parallel-fed SET project -- think I found it in an old tube radio manual I have. The choke (around 10 H I believe or a bit more...)is placed in series with the plate and B+. The choke offers both very low DCR and opposition to the signal, and the voice coil is fed by way of the capacitor (several mfd.). The design constraint I see with this if applied to hi-fidelity audio has to do with modern voice coil impedance matching. Audio output stages in old receiving radios had very high output impedance (few thousand ohms), but were coupled to loudspeaker voice coils (often in headphones) of equally high impedance. The Radiola horn speakers I have use voice coils (one is a modern replacement)of about 2K ohms.

I think the implication of this sort of output approach points toward what we now know as OTL amplification. Separating the DC and AC components, as can be achieved with the also very old parallel feed approach, may have distinct advatages over the use of a single transformer that must deal with both of those elements simultaneously. But in the case of high quality reproduction of music at home, however, and up until the now fairly common use of OTL designs, it seems that there was no other way of (literally!) getting around the use of an voice-coil/output-tube-plate impedance matching transformer. in the first few decades of the 1900s, Western Electric arrived at an ingenious way of separating signal and power supply components (Jack Eliano's 'Ultrapath'), so it seems that a great deal of thought and engineering has gone into trying to effectively separating the necessary direct and alternating current components in audio amplification stages.

This is the primary reason that OTL designs seem to me to be very close to the ideal way of coupling music signals to modern loudspeakers of comparatively lower impedance.

Thank you for including and mentioning the choke-capacitor output technique -- it continues to intrigue me, regardless (or because!) of how old it is!

Erik

Also, although I'm not a technician or an engineer by trade, I enjoy learning 'how things work' and I approach anything that someone claims to be 'new' or 'original' with a large dose of skepticism.

Some say that history will repeat itself, for which I ask myself if that means that anything 'new' or 'original' in audio is just history that I don't know about?

It seems that most 'originality' in audio is only something 'we' haven't seen or heard, which means to me that those classics, or soon to be classics, that stand the test of time may only be a credit to the execution or implementation of previous ideas, rather than their originality.

Edited June 22, 2014 by Fjd

[Fjd]

Jack Eliano also contributed to Vacuum Tube Valley. That's where I believe he first shared his schematic and discussed the DRD, so-called, design, it uses an unusual connection on the output, as also does the parallel or shunt feed we discussed previously, but is not the same. He calls it "Ultrapath". Also like parallel feed outputs, the Ultrapath was done a very long time go by.....who was it...Western Electric? General Electric? Can't remember which, now. I had done research into the technique, and it is quite old. The so-called Ultrapath capacitor is the large one (motor run type) shown under the chassis in the Electra-print amplifier. Eliano stated in the VTV article that he thought those capacitors were measurably more sensitive to low level detail, and having built both a DRD 45 and DRD 2A3, would say that detail retrieval is certainly one of the characteristics of the circuit.

Actually, here is a better description that is in my DRD/Ultrapath project folder.

I think just a little more clarification is in order for others who may read this:

The term 'Ultrapath' is a term which was first used by Jack Eliano, of Electra-Print (company that makes audio transformers, chokes, etc.)Jack Eliano is the guy who designed the DRD amplifiers now offered by Welborne Labs. This so-called 'Ultrapath' connection is not new, having first been used by Western Electric years and years ago. It wasn't even called 'Ultrapath' then. It is just a really smart way of changing the position and type of capacitor that normally is connected across (bypassing)the cathode bias resistor -- in the 2A3, this is a high wattage power resistor.

In a conventional output connection that DOES use a bypass capacitor across the cathode bias resistor, one end of the output transformer primary is connected to the plate of the output tube, and the other leg of the primary is connected (or returned) to the power supply. Jack Eliano's Ultrapath connection, the approach first used by W.E., returns the signal from the transformer to cathode instead of the power supply to cathode, which theoretically should offer better detail, less noise, etc. One of the more important advantages to this technique is that it effectively removes all electrolytic capacitors from the signal side of the circuit. That's why when cathode resistor bypass capacitors ARE used (as in a more tradtional SE output connection), it's good to use very high quality electrolytics. The Moondog, however, uses a lower value poly tubular capacitor in that position.

I wanted to build the DRD amps a few years ago, but couldn't afford the transformers for them. It suddenly dawned on me that the Moondog would be a good candidate to try that 'ULTRAPATH' connection -- and so I did it. The thing was that, despite the fact that this can be done on a single-ended amplifier, there were other important aspect on the DRD design that make it quite a bit different from the Moondogs.

Leok then tried the W.E. connection and really liked it. But he also had the insight (for which he deserves credit and thanks)to take this a step further -- and that further step being the employment of a parallel or shunt feed output in conjunction with the change in position of the cathode resistor capacitor. And this is the part that is of interest to me: Whether the W.E. (aka Ultrapath) connection behaves the same way with parallel feeding as it does with regular single-ended output transformer. In theory, it should. Parallel feeding basically frees the output transformer from having to 'pull two shifts'at the same time -- kind of like killing two birds with one stone (poor birds! My dad used to say to me, "You shoot it, you eat it!") I loved making different kinds of slingshots when I was a kid.

So, that's some of the deal with the 'Ultrapath' connection.

The other place a cathode bias resistor bypass capacitor (one with a lower voltage rating)is often used is on the input of the circuit. On the Horus, this is the 5687 tube -- a little guy compared to the big 2A3. The Horus does not use a capacitor in that position (it is not mandatory), nor does Leo on his Moondogs. Some have reported that they prefer the sound with the cap, others say it makes music sound a little less lively. What I'm hoping for, which among the main reasons the capacitor is used, is just a little more gain, which may translate into just a little more weight or heft to the presentation. I won't accept an alteration in the current high speed ability of this phenomenal amplifier, though. If the capacitor effects that characteristic in any way, it's coming out! I far prefer an airy and open sound to one with more bass -- I don't listen to music at really loud volume, anyway. If Segovia happened to be sitting in my listening room playing his guitar, I would want the volume level of playback from a CD or record to be similar.

So.

The End

[Schu]

Speaking of biasing (check out the battery of pots) and some very nice Japanese OTL amp point-to-point wiring -- for those who appreciate skilled vacuum tube wiring and craftsmanship:

http://www.miyajima-lab.com/e-amp.html

Quite beautiful work, I think. Stereophile's Art Dudley really liked these amps.

Nicely made. It's one of those pieces which has a crafter's aesthetic to it as well as maybe being a nice sounding amplifier too. I however, don't believe this is usually a good deal for consumers. It's not the way I like to play it. Paying a little guy to sit and route wires is a total extravagance. Like buying a hand made car.

I don't think that is really what we're talking about here at all. this point is not a discussion about design or build quality from a price point sensitive perspective, this was merely pointing out the care that was taken to lay out a wiring harness correctly.

That clean layout show's respect, care and exhibits a quality for the customer's amplifier that a rats nest of wiring simply can not.

Does it take more time, planning and is a SLIGHTLY more costly because of this, of course... but it's not a Timex vs Patek Phillipe. it's more akin to a Timex built in a factory in Ohio and a Timex built in a studio in Japan.

Edited June 22, 2014 by Schu

[erik2A3]

FJD: Gosh, I haven't seen those old posts of mine since the time I wrote them, but I had forgotten they went back as far as 2003. When I first tried logging in again after a long while with my old handle (Erik Mandaville), I wasn't able to get in...some things had changed; I had forgotten my password, etc. So, just out of curiosity, I started completely fresh using erik2a3 instead, and it worked! So I stuck with it. Thank you for posting that interview with Jack E. Very interesting! I talked with him on a couple of occasions some years ago -- he's a very friendly person, as well as a talented artist (as in actual painting and drawing....in addition, of course, to amplifier design).

Sheesh, I have several single ended amps around here I could rebuild as DRD Ultrapaths -- I'm very tempted to do a 300B version! Edit: I dug around through my old stacks of VTV, a Glass Audio, a Speaker Builder, etc., and found the original DRD 300B schematic published for personal, non-commercial use. Jack E's description of all parts sort of shaking hands with one another is a good way to describe the circuit. If I remember correctly, this is around the time Welborne Labs (who was already using Electra-Print transformers) began selling the DRD kits -- and very well put together kits they were, too. They were done better, in my opinion, than the older Moondogs (which I still have).

Edited June 23, 2014 by erik2A3

[tube fanatic]

But so to was the build quality of the enormous WWII era Hallicrafters and Hammarlund receiving and transmitting radios -- which were built and soldered together by extraordinarily skilled workers, many of whom were women.

Erik, I can't agree with you more. Having worked on countless pieces of pre and post WWII Hammarlund, Hallicrafters, and National gear I can say that they were all engineering masterpieces assembled to a level of quality which still amazes me. It's one of the reasons that these companies eventually went under as they built things so well that there was little reason for owners to upgrade. In terms of modern wiring techniques and build aesthetics though, I keep coming back to Leben. I find their under-chassis work to be something I still aspire to duplicate in my own creations!

http://lebenhifi.com/products/products-img/cs300x_down_l.jpg

It also brings to my mind the modern work ethic which often eschews such build quality. When I worked for the industrial power supply company, one of my colleagues was in charge of constructing refrigerator sized switching power supplies (we're talking as much as 4000V at 20,000+ A). His wiring harnesses were examples of perfect symmetry, alignment, even spacing of tie wraps, and most importantly connections which never failed. They were both visual and electromechanical works of art. The owner of the company told him that he was wasting his time making things look so beautiful and eventually reassigned him to hands-off activities. Personally, I think it was a terrible mistake to do that. One of my own jobs (when not working on electromechanical layouts), was to construct power supply control panels and, of course, I employed the same build philosophy. The owner didn't like that either as it made the work turned out by the other guys look positively shoddy in comparison. He asked me to build the way they did- I said "no way" and was fired!!!

Maynard

[erik2A3]

Maynard: I am impressed. I am not the same as you; I have worked on a couple of those old radios...and that's all. I have a few of them in my collection, though, and just think they are very special. The problem now, however, is that very few of the shortwave stations to which I used to listen even broadcast anymore. Even BBC has changed, in my view not necessarily for the better. But that's just me missing the old and traditional formats. Everything changes.

I am very impressed with your description of industrial power supplies, and would run with my tail tucked at 4k+ Volts! I can do no more than respect your integrity for correct and neat wiring of whatever you worked on. Erik M.

[erik2A3]

And Maynard: I just checked the link you attached. Very nice, indeed!

[mike stehr]

Yep...If I disposable income, I'd definitely check out the Leben EL-84 integrated.

[paul79]

Siquerra or Sid, one or the other, was the one responsible for taking the hum out of the early Marantz tube designs, that Saul could not do... I'll get the correct story and share... I am good friends with the owner of the prototype 10 tuner, and he knew Saul very well.

[Schu]

Correct- all that kind of wiring was perfected as an assembly line technique. During that era of say post WWII up to the mid 1960s or so, that was the best practice and considered lowest cost manufacturing. The PCB slowly replaced all that because the cost advantage could not be ignored, and the repeatability was better. There are also some technical benefits over hard wires, like the ability to have ground planes.

Let's not forget that the PCB was a direct result of the Apollo program... and while all the things you mention are true, the program used them in part because of the resistance to shock.

[NOSValves]

A question which I've not been able to have answered is whether modern push-pull tube amps with autobiasing also have that feature applied to the phase inverter.

I don't know which commercial products might have it, but it's an easy circuit to implement at the phase inverter stage. We can thank Bleumein again for the principles of how it is done, and then we can thank technology for providing inexpensive and very powerful parts for accomplishing it.

No question that there are devices available which make automatic balancing easy to implement. Personally though, I try not to use anything solid state in my amps (other than the diodes in the p/s) due to their failure rate when exposed to powerline surges and spikes. Back in my TV repair days I attributed many, if not most, failures to such events and sometimes went as far as installing MOVs for suppression (I have a friend, an ex-Army ET, who collects TVs which people put out with their garbage and repairs them for sale at his church's rummage sales- he too feels that the SS components which he finds fried took a powerline hit). The tube type TVs weren't susceptible to anywhere near the degree of the solid state types. I have to wonder why the manufacturers of amps employing numerous solid state devices don't spend the few cents to stick MOVs in there as well. Maybe it's because they want to have the built-in obsolescence by not doing so. I can't imagine it's because they assume that everyone uses an external surge/spike protector. The lack of a channel balance control (pot or solid state) in so many modern amps is another factor which amazes me!

Maynard

Another great post! I agree 200% but I will add that these very same spikes can come from tube failure and take out the same parts......I have had the joy and pain of working on many modern over engineered gear from some pretty heavy hitters in tube Hi Fi. In every single case the failure was traced back to solid state devices.....some were a real pita to source an appropriate replacement since the parts were obsolete but the device they were used in was not all that old. The trick many of these companies employ is the buy up all the obsolete parts and ten hold you ransom charging 1000% or higher mark ups if they will sell you it at all.

Edited June 23, 2014 by NOSValves

[paul79]

Yep, I believe you are correct. I'll see my buddy on Friday and get the scoop. That Model 10 prototype tuner is very cool also. Quite different than the production versions. I believe he was offered $20K for it at one time. Really neat piece of history.